This invention is directed to a composition and method for treating anal disorders such as anal fissure, anal ulcer, hemorrhoidal disease and levator spasm, by topical application of the composition to or proximate the affected area.
In general, anal fissure (fissure-in-ano), anal ulcer, acute hemorrhoidal disease, and levator spasm (proctalgia fugax) are common, benign conditions of the anal canal which affect humans of all ages, races and sexes. However, these conditions can be problematical to treat and inconvenient if not painful to endure. An anal fissure or ulcer is a tear or ulcer of the mucosa or lining tissue of the distal anal canal. Anal fissure/ulcer can be associated with other systemic or local diseases but is more frequently present as an isolated finding. The typical, idiopathic fissure or ulcer is confined to the anal mucosa, and usually lies in the posterior midline, distal to the dentate line. The person with an anal fissure or ulcer frequently experiences anal pain and bleeding, the pain being more pronounced during and after bowel movements.
Hemorrhoids are specialized vascular areas lying subjacent the anal mucosa. Symptomatic hemorrhoidal disease is manifest by bleeding, thrombosis and/or prolapse of the hemorrhoidal tissues. Commonly, internal hemorrhoidal tissue bulges into the anal canal during defecation causing bleeding and pain. As the tissue enlarges, further bleeding and pain, prolapse and thrombosis can ensue. The thrombosis of hemorrhoids is another cause of bleeding and pain.
Levator spasm is a condition affecting women more frequently than men. This syndrome is characterized by spasticity of the levator ani muscle, a portion of the anal sphincter complex. The patient suffering from levator spasm may experience severe, episodic rectal pain. Physical exam may reveal spasm of the puborectalis muscle and pain may be reproduced by direct pressure on this muscle. Bleeding is normally not associated with this condition.
The underlying causes of these anal disorders are poorly understood, but all of these conditions are associated with a relative or absolute degree of anal sphincter hypertonicity. In the case of anal fissure/ulcer, the abnormality appears to be an as-yet-unidentified problem of the internal anal sphincter muscle. The internal sphincter is a specialized, involuntary muscle arising from the inner circular muscular layer of the rectum. Intra-anal pressure measurements obtained from people suffering from typical anal fissure/ulcer disease show an exaggerated pressure response to a variety of stimuli. The abnormally high intra-anal pressure is generated by the internal sphincter muscle and is responsible for non-healing of the fissure or ulcer and the associated pain.
An abnormal pressure response in the anal canal has also been observed in people suffering from symptomatic hemorrhoidal disease. Elevated intra-anal pressures may be a major factor in the development of this condition. It has been postulated that the pain associated with acute hemorrhoidal disease is caused in part by spasm of the internal anal sphincter muscle. Similarly, the pain associated with levator spasm is induced by the muscle spasm itself.
Various therapies have been devised to treat these anal disorders. Typical, non-surgical therapy includes bulk laxatives and sitz baths. Sitz baths are helpful because they induce relaxation of the anal sphincter mechanism. See e.g., Shafik, “Role of warm-water bath in anorectal conditions: The ‘thermosphincteric reflex,’ ”J. Clin. Gastroenterol., 16:304–308, 1993.
Topical anal therapy is also used in an effort to promote healing, relieve pain, and reduce swelling and inflammation. Many preparations have been tried including those containing local anesthetics, corticosteroids, astringents, and other agents. However, none of these preparations has been shown conclusively to reduce the healing time or to reliably ameliorate associated pain.
In certain instances, surgery may be employed to treat anal disorders. Cases of anal fissure/ulcer or hemorrhoids recalcitrant to medical therapy are often referred for surgical treatment. In keeping with the proposed etiology of anal fissure/ulcer, the current standard surgical procedure therefor is lateral internal anal sphincterotomy. In this procedure, the internal anal sphincter muscle is partially cut, thereby reducing the intra-anal pressure. The lowered pressure allows the fissure/ulcer to heal and also relieves the associated pain. Surgical hemorrhoidectomy removes the redundant hemorrhoidal tissue, and many surgeons will perform concomitant limited internal anal sphincterotomy to lower anal canal pressure. There is no successful surgical treatment for levator spasm.
Recently, a third component of the autonomic nervous system, known as the enteric nervous system (ENS), has been described and elucidated. This neural network innervates the gut continuously from esophagus to anus. It is composed of enteric neurons, and the processes of extrinsic efferent and afferent neurons of the traditional autonomic system. This system regulates the motor and secretory function of the gut. A notable feature of the ENS is the diversity of chemical messengers which enteric neurons contain and release. In addition to acetylcholine and norepinephrine, various peptide and non-peptide substances have been identified which appear to function as neurotransmitters in the ENS. Inhibitory non-adrenergic non-cholinergic (NANC) nerves are thought to be important therein.
More recently, nitric oxide (NO) has been identified as an inhibitory transmitter to muscle. It has been shown that NO mediates the anorectal inhibitory reflex in animals and man. See e.g., Rattan et al., “Nitric oxide pathway in rectoanal inhibitory reflex of opossum internal anal sphincter,” Gastroenterology, 103:43–50, 1992; Chakder et al., “Release of nitric oxide by activation of nonadrenergic noncholinergic neurons of internal anal sphincter,” Am. J. Physiol., 264:G7–G12, 1993; O'Kelley et al., “Nerve mediated relaxation of the internal anal sphincter: The role of nitric oxide,” Gut, 34:689–693, 1993. See also, Gillespie et al., “Influence of haemoglobin and erythrocytes on the effects of EDRF, a smooth muscle inhibitory factor, and nitric oxide on vascular and non-vascular smooth muscle,” Br. J. Pharmacol., 95:1151–1156, 1988; Ignarro et al., “Nitric oxide and cyclic GMP formation upon electrical field stimulation cause relaxation of corpus cavernosum smooth muscle,” Biochem. Biophys. Res. Commun., 170:843–850, 1990; Bult et al., “Nitric oxide as an inhibitory non-adrenergic non-cholinergic neurotransmitter,” Nature, 345:346–347 1990. It has been proposed that NO formation, based upon non-enzymatic NO release from various organic nitrates as catalyzed in the presence of cysteine, causes direct or indirect activation of the soluble guanylate cyclase, finally resulting in relaxation of vascular smooth muscle in vivo. See, Feelisch et al., “Correlation between nitric oxide formation during degradation of organic nitrates and activation of guanylate cyclase,” Eur. J. Pharmacol., 139:19–30, 1987. See also Fung et al., “Biochemical mechanism of organic nitrate action,” Am. J. Cardiol., 70:4B–10B, 1992.
Organic nitrates such as nitroglycerin (GTN), isosorbide dinitrate (ISDN), isosorbide mononitrate (ISMN), erythrityl tetranitrate (ETN), pentaerythrityl tetranitrate (PETN) are known to cause vasodilation and have been used for decades in the treatment of angina pectoris. See e.g., Huff et al. (Eds.), “Physicians' Desk Reference,” 41st Edition, Medical Economics Company, Oradell, N.J., 1987, at pages 780, 1176–78, 1533 and 1984–85; Rubin, U.S. Pat. No. 5,059,603 (October 1991); Budavari et al. (Eds.), “The Merck Index,” 11th Edition, Merck & Co., Rahway, N.J., 1989, p. 821 (isopropyl nitrate); Fung et al., “Biochemical mechanism of organic nitrate action,” Am. J. Cardiol., 70:4B–10B, 1992.
Corticosteroids such as hydrocortisone have been used for the treatment of various benign anal disorders for many years. Studies of this treatment have show some benefit thereby but not in a reproducible nor significant fashion.
Topical anesthetics such as dibucaine, lidocaine, pramoxine, and others have been used for treatment of anal pain. However, any relief has been relatively short-lived.
Various other preparations are known. See e.g., Suzuki et al., U.S. Pat. No. 4,292,299 (September 1981), note column 5 lines 18–20 & 26–28; Rubin '603, note column 7, lines 61–65 & example 1; Greiner, U.S. Pat. No. 5,183,663 (February 1993). See also, Williams, U.S. Pat. No. 4,118,480 (October 1978); Huff et al. (Eds.), “The Merck Index,” 11th Edition, page 198.